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F. W. E RRITT, AIR COMPRESSOR. No. 562,475. PatentedJune 23,1896.

ANDREW B.GRAHAM.FHDTO'UTMO WA$HING1DNYDC UNITED STATES PATENT OFFICE,

FRANK MERRITT, OF DULUTH, MINNESOTA, ASSIGNOR TO THE ELECTRIC MOTORCOMPANY, OF SAME PLACE.

AlR-COMPR'ESSO R.

SPECIFICATION forming part of Letters Patent No. 562,475, dated June 23,1896.

Application filed December 2, 1892. Serial No. 453,825. N model.)

To all whom it may concern.-

Be it known that I, FRANK W. MERRITT, of Duluth, in the county of St.Louis and State of Minnesota, have invented certain new and usefulImprovements in Air-Compressors; and I do hereby declare that thefollowing is a full, clear, and exact description of the inventiomwhichwill enable others skilled in the art to which it pertains to make anduse the same, reference being had to the accompanying drawings, and tothe letters of reference marked thereon, which form apart of thisspecification.

The main objects of my invention are to prevent the air-pressure fromrising above a certain predetermined point without stopping orinterrupting the operation of the pump, and to avoid undue heating ofthe pump-cylinder and associated parts.

It consists, essentially, of auxiliary reliefvalves communicating withthe ends of the pump-cylinder and connected with pistons exposed. to thepressure produced by the pump, and of certain novel features ofconstruction and arrangement of parts, hereinafter particularlydescribed, and pointed out in the claim.

In the accompanying drawings like letters designate the same parts inthe several figures.

Figure 1 is a side elevation and partial vertical section on the line 11, Fig. 2, through the compressed-air chamber and valve-chambers at oneend of a pump embodying my improvements. Fig. 2is ahorizontal section ofthe same on the line 2 2, Fig. 1. Fig. 3 is a vertical cross-section onthe line 3 3, Fig. 2; and Figs. 4. and 5 are inverted plan views of thevalve-cages at one end of the pumpcylinder.

A represents the pump-cylinder, provided, as shown in Fig. 2, with apiston B, fixed upon a piston-rod O, which passes through a suitablestuffingboxin one of the cylinder-heads in the usual manner. Thecylinder is cast or otherwise provided on one side with a compressed-airchest or chamber D, having a discharge opening or connection d, and ator near each end with valve-chambers E E, adjoining chamber D andcommunicating with the ends of cylinder A through ports 6. In thechambers E E are fitted and held by screw-threaded connectionsvalve-cages F, which open at their inner ends into the compressed-airchamber D, at their outer ends through a number of small holes f fintothe outside atmosphere, and at intermediate points through lateralopenings or ports f f into the valve-chambers E E, in which they areinserted. Each of these cages is formed or provided at its inner end,and between the ports f and its outer end, with valve-seats for inletand outlet valves G and H, the inlet-valve opening inwardly from theouter end of the cage toward the port f and the outlet-valve openingoutwardly from the port f into the compressed .air chamber D. 1

. I I arereliefq-alve chambers adjoining the compressed-air chamber Dand the valvechambers E E at each end of the cylinder, and communicatingwith the latter through ports '5. In these chambers I I are inserted,and held byscrew-threaded connection, cages J, opening at their innerends into the compressed-air chamber D, and at their outer ends into theexternal atmosphere. They are provided at their outer ends withscrewthreaded caps j j, having a number of small air-inlet holes 3" j,and are formed with lateral openings or ports j j communicating with thechambers I I, in which they are inserted.

Each of the cages J is provided with an outwardly-opening relief-valveK, which has a seat therein justbelow or outside of the ports j". It isheld normally to its seat by a spring 7a, the tension of which isadjusted by a screw in cap To the upwardly-projecting stem of each ofthe relief-valves K is fixed a piston L, which is fitted and adapted towork within the cage J between its inner end and ports 7' My improvedair-compressor operates as follows: As the piston B moves from one endtoward the other end of cylinder A, it tends to produce vacuum in thatend of the cylinder from which it is moving, thereby 0pening theinlet-valve G at that end of the cylinder and permitting air to enterthrough the same from the outside. At the same time the air contained inthe other end of the cylinder, toward which the piston is moving, willbe forced through ports 6 and f, and, opening the outlet valve H, willenter chamber D. When the movement of the piston is reversed, theadjacent outlet-valve H will be closed and the inlet-valve G opened,While the outletvalve II at the opposite end of the cylinder will beopened, and the corresponding inletvalve closed, during the returnstroke of the piston. Thus the reciprocation of the piston alternatelyopens and closes the inlet and outlet Valves G and H at opposite ends ofthe cylinder, admitting air from the outside into that end of thecylinder from which the piston is moving, and forcing it from that endto- Ward which it is moving, into the chamber D. The tension of thespring 70 having been adjusted, by means of the screw 70, to sustain,for example, a pressure of fifty pounds per square inch, when theair-pressure in chamber D for any cause rises above that point, actingupon the pistons L it will open the relief-valves K, thus admittingoutside air through the holes j and ports 7' 1', f, and 0 into one endof the cylinder, and permitting the air to be discharged from the otherend of the cylinder in the reverse direction through the correspondingports and openings, without increasing the pressure in chamber D. Freshoutside air being thus drawn into and immediately discharged from thecylinder tends to cool it. pistons L becomes less than the tension ofspring 76, the relief-valves K will be autom atically seated, and thepump will resume its 11 ormal' action.

The inlet and outlet valves, as herein shown As soon as the pressure onand described, are constructed and arranged to be seated by gravity; butthey may be otherwise closed and held to their seats. In short, variouschanges in the details of construction and arrangement of the componentparts of my improved compressor may be made within the spirit of myinvention.

I claim In an air-compressor, the combination with the piston and thecylinder formed or provided with an air-chest, and with adjoiningvalve-chambers communicating with each other and with the ends of thecylinder-of cages inserted in said chambers, and opening at the endsinto the compressed-air chamber and into the outside air, and atintermediate points into the valve-chambers in which they are inserted;inlet and outlet valves seated FRANK W. MERRITT.

lVitnesses:

OnAs. A. ToWNn, J. D. ELLIs.

